Difluorobenzene‐Based Locally Concentrated Ionic Liquid Electrolyte Enabling Stable Cycling of Lithium Metal Batteries with Nickel‐Rich Cathode

Abstract Lithium metal batteries (LMBs) with nickel‐rich cathodes are promising candidates for next‐generation, high‐energy batteries. However, the highly reactive electrodes usually exhibit poor interfacial compatibility with conventional electrolytes, leading to limited cyclability. Herein, a locally concentrated ionic liquid electrolyte (LCILE) consisting of lithium bis(fluorosulfonyl)imide (LiFSI), 1‐ethyl‐3‐methylimidazolium bis(fluorosulfonyl)imide (EmimFSI), and 1,2‐difluorobenzene (dFBn) is designed to overcome this challenge. As a cosolvent, dFBn not only promotes the Li + transport with respect to the electrolyte based on the ionic liquid only, but also has beneficial effects on the electrode/electrolyte interphases (EEIs) on lithium metal anodes (LMAs) and LiNi 0.8 Mn 0.1 Co 0.1 O 2 (NMC811) cathodes. As a result, the developed LCILE enables dendrite‐free cycling of LMAs with a coulombic efficiency (CE) up to 99.57% at 0.5 mA cm −2 and highly stable cycling of Li/NMC811 cells (4.4 V) at C/3 charge and 1 C discharge (1 C = 2 mA cm −2 ) for 500 cycles with a capacity retention of 93%. In contrast, the dFBn‐free electrolyte achieves lithium stripping/plating CE, and the Li/NMC811 cells’ capacity retention of only 98.22% and 16%, respectively under the same conditions. The insight into the coordination structure, promoted Li + transport, and EEI characteristics gives fundamental information essential for further developing (IL‐based) electrolytes for long‐life, high‐energy LMBs.